Fix bubble visibility issue when collapsed

When the bubble bar collapses, explicitly set the alpha to 1
for bubbles that should not be hidden.

Flag: com.android.wm.shell.enable_bubble_bar
Fixes: 345283193
Test: manual
       - create 3 bubbles in the bar
       - tap to expand
       - select the last bubble
       - tap it again to collapse
       - observe it is visible
Change-Id: I1aed310b66433b88b08ccaf760fc8e82923b1b64